This invention relates to inserts for closures of the press-on/twist-off type which have a tamper evident band.
Press-on/twist-off closures are caps which not only are applied to and removed from a container by press-on and twist-off actions respectively but which also comprise a tamper-evident band. Such closures are sometimes known commercially as PT+ (trade mark) closures.
Press-on/twist-off (PT) closures are well known in which the closure has an insert formed from a foamed plastisol material. PT+ closures have been described, for example, in EP-0450959 in which the closure comprises a metal body lined with a plastisol gasket and having a tamper-evident band (also known as a xe2x80x9csecurity ringxe2x80x9d).
In WO 98/52833, a press-on/twist-off closure is described which uses a pre-formed insert in place of the former plastisol material. Instead of moulding the insert in the closure shell, as with a foamed plastisol material, the insert of WO 98/52833 can be formed separately by injection moulding, for example, and then secured in the shell by a curl on the edge of the shell.
The insert of WO 98/52833 is formed from a relatively soft material such as certain grades of polypropylene, polypropylene/nylon blends or thermoplastic elastomers. Soft liners provide excellent sealing since they readily conform to irregularities in the sealing surface and threads in the finish of a glass container to which the closure is applied. However, problems arise when applying the closure since the insert may flex if the press-on capping action is not applied in a truly horizontal position. This problem can be further exacerbated if a tamper evident band is to be used in conjunction with the soft insert, as the liner is free to move in the metal shell when the tamper evident band is applied. This can lead to rotation and/or tilt of the insert.
A further problem exhibited by the insert of WO 98/52833 is the difficulty in handling a flexible component at commercial line speeds in current cap manufacturing apparatus. Twisting of the component into loops and asymmetric shapes is typical in addition to problems of presenting the insert to the closure shell in the correct orientation.
This invention seeks to provide a pre-formed insert for a closure which overcomes these problems.
According to the present invention, there is provided a pre-formed moulded insert having a first portion formed of a polymeric material having a Shore hardness in the range of 30 Shore A to 45 Shore D, and a second portion comprising a tamper evident band integrally formed with the first portion and formed of a polyolefin material.
Typically, the material of the second portion has a flexural modulus greater than 1200.
In a further aspect of the present invention, there is provided a closure of the press-on/twist-off type comprising a shell including a skirt and an end panel, and a pre-formed insert of the type described above, in which the first portion is adapted to perform liner and sealing functions in the closure, in which the insert is secured in position with the first portion within the closure such that the tamper evident band depends from the closure shell.
For sealing a container, the thread finish on the container may form complementary threads on the inner side wall of the insert when the closure is applied to the container and the gasket part of the insert provides sealing between the end panel of the closure and the end sealing surface of a neck finish. The insert of the present invention thus provides (i) a gasket function, (ii) a thread forming feature and (iii) a tamper evident band, in a single component.
By using an insert which includes an integral tamper evident band prior to assembly in the metal shell, risk of tilting or rotation of the sealing/liner portion is eliminated. The unitary construction of the insert of the present invention means that there is only ever a single component to be secured in position.
The insert may be secured in position within the shell by curling the edge of the metal shell into or around part of the insert, thermal or other bonding, or by other mechanical means of engagement.
In a preferred embodiment, the tamper evident band portion comprises a material having a flexural modulus of between 1200 and 1600 MPa. By using a stiffer material for the tamper evident ring portion of the insert, rigidity is provided to the whole insert. This in turn makes the insert easier to handle by maintaining it in a circular (rather than twisted) shape, easier to position within the closure shell and, when inserted in the closure shell, easier to apply to a container in the required horizontal position.
The insert may be formed by sequential (two colour/two material) moulding of a plastic component from two portions having properties selected according to the portion of the insert for which the material is intended. Usually the material of the second portion may be polypropylene or polypropylene-based. Conventionally polymers such as polypropylene is characterised by its modulus.
The material of the first portion may be a polypropylene blend including materials such as butyl rubber, nitrile rubber, EPDM, ethyl vinyl, polyurethanes, acrylic polymers, polyethylenes and copolymers, or nylons. Conventionally, such elastomers are defined by their Shore hardness. The choice of material used for the first portion depends on the ability to mould a single component from two materials with different Shore hardness/flexural moduli according to the function to be performed.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings in which: